Real-time monitoring of the position and orientation of handheld and/or fully automated surgical tools has been hampered by a lack of low-cost accurate sensors. Optical tracking, e.g., detection of reflective or light emitting markers associated with the tool, has been proposed but requires clear line of sight to function accurately. Additionally, high bandwidth (high sampling rate) optical sensor systems are often prohibitively expensive. However, less expensive optical systems, for example, those with sampling rates of about 60 Hz, are often unacceptable for guided controlled surgical instruments because they track too slowly. This can make it difficult or impossible to use guided instruments requiring a fast and accurate response, such as a controlled burr or shaver tool. Instead, a cutting guide is often required, the installation and removal of which can unduly lengthen the time duration of the surgery. Electromagnetic tracking systems can also be unacceptable for many of the same reasons.
Inertial sensor systems, e.g., involving sets of three gyroscopes, three accelerometers and optionally, three magnetometers, can inexpensively provide rapidly updated signals indicative of surgical instrument movement. Sampling rates of up to 500 Hz are practical at low cost but such systems are not reliable due to noise and signal drift associated with such inertial sensors.
Hybrid systems combining two or more types of sensors have been proposed by others. See, for example, U.S. Pat. No. 6,611,141 issued to Schulz et al. on Aug. 26, 2003 entitled “Hybrid 3-D Probe Tracked by Multiple Sensors,” the entire contents of which are incorporated herein by reference.
There exists a need for better methods and systems for object tracking and, in particular, better methods and systems for determining the position and orientation of surgical instruments in three-dimensional space to assist in navigated surgery. Inexpensive methods and systems that could permit position and movement tracking with rapid updates, e.g., at rates greater than 300 Hz, would satisfy a long-felt need in the art.